杭电 小希的迷宫 （并查集）

#include <iostream>
using namespace std;
#define MAX 100010
int mark[MAX], set[MAX];

int find(int n)
{
return set
==n?n:find(set
);
}
int Unioun(int u, int v)
{
int x, y;
x = find(u);
y = find(v);
if (x!=y)
{
set[x] = y;
return 1;
}
else
return 0;
}
int main()
{
int u, v, flag, nc, i;
while (1)
{
flag = 1;
memset(mark, 0, sizeof(mark));
while (cin>>u>>v && (u!=-1&&v!=-1))
{
if (u==0&&v==0) //0 0 也是树
{
cout<<"Yes"<<endl;
continue;
}
for (i=0; i<MAX;  i++)
set[i] = i;
int max=-1, min=MAX;
while (u||v)
{
if (u>max) max=u;
if (v>max) max=v;
if (u<min) min=u;
if (v<min) min=v;
mark[u] = mark[v] = 1;
if (Unioun(u, v)==0) //判断是否能连接上
flag = 0;
cin>>u>>v;
}
if (flag==0)
cout<<"No"<<endl;
else
{
nc = 0;
for (i=min; i<=max; i++)
{
if (mark[i]&&set[i]==i)//记录是否只有一棵树
nc++;
}
if (nc==1)
cout<<"Yes"<<endl;
else
cout<<"No"<<endl;
}
}
if (u==-1 && v==-1)
break;
}
return 0;
}